1. Field of the Invention
The present invention relates to an apparatus for measuring distortion of a cylindrical body which is suitably used for measurement of radial distortion of a cylindrical body, such as an inner or outer ring of a bearing.
2. Description of the Related Art
In general, when an inner ring Ci or an outer ring Co of a ball bearing M shown in FIG. 8 has a distortion in the radial direction, a raceway groove Cis or a groove Cos for guiding balls B exhibits waviness. When such a ball bearing M is used, axial vibration is generated, making smooth and stable rotation unattainable. Therefore, distortions of the inner ring Ci and the outer ring Co must be minimized. That is, when the inner ring Ci is rotated one turn with the position of its lower end surface Cid fixed, radial distortion Ed as measured at an upper end surface Ciu of the inner ring Ci ideally becomes zero. However, in actuality, some distortion Ed is present and must be reduced to a specified tolerance.
Incidentally, such distortion Ed has conventionally been measured by use of an electronic micrometer as disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 8(1996)-261710. FIG. 9 shows a conventional distortion measurement apparatus 60 capable of measuring distortion Ed by use of an electronic micrometer. The distortion measurement apparatus 60 has a holding plate 62 which is disposed on the top face of a base block 61 and has a V-shaped holding depression 62s. A peripheral surface of a lower end of a cylindrical body C (e.g., an inner ring Ci) is brought into contact with the holding depression 62s. A probe 63s of an electronic micrometer 63 is brought into contact with an upper portion of the peripheral surface of the cylindrical body C at a position diametrically opposite the holding depression 62s. During measurement, after a conical portion 64 of a rotation jig 65 is pressed against an inner edge of the cylindrical body C, an operator rotates the cylindrical body C over one turn, and obtains distortion Ed from variation measured by the electronic micrometer 63. When the thus obtained distortion Ed falls outside the specified tolerance, the operator judges the cylindrical object to be defective.
However, such a conventional distortion measurement apparatus 60 has the following drawbacks.
First, because of mechanical contact involved in measurement, measurement error increases, especially in measurement of a small cylindrical body C, such as a small inner ring Ci whose outer diameter is not greater than several millimeters. Therefore, precise measurement cannot be performed with high reproducibility.
Second, since a major portion of measurement work must be performed manually by an operator, measurement requires time and labor, and stable, reliable measurement cannot be performed.
An object of the present invention is to provide an apparatus for measuring distortion of a cylindrical body which eliminates mechanical contact and enables performance of precise measurement with high reproducibility.
Another object of the present invention is to provide an apparatus for measuring distortion of a cylindrical body which facilitates realization of fully-automated operation, eliminates manual operation, and enables stable, reliable measurement.
In order to achieve the above objects, an apparatus for measuring distortion of a cylindrical body according to the present invention includes: a stationary straight rail provided on a flat surface; a cylindrical-body transfer mechanism for rolling the cylindrical body such that a peripheral surface of one end of the cylindrical body remains in contact with the stationary straight rail; a reference pole disposed at a position separated a predetermined distance from the cylindrical body in a direction perpendicular to the rolling direction of the cylindrical body; a laser scan micrometer capable of simultaneously scanning the other end of the cylindrical body and the reference pole by means of laser beam projected toward the rolling direction to thereby measure a distance between the cylindrical body and the reference pole; and a control section for controlling the cylindrical-body transfer mechanism and the laser scan micrometer and for processing measurement data output from the laser scan micrometer to thereby obtain distortion. By virtue of the above-described configuration, radial distortion of the cylindrical body can be measured.